Cursors opened on checkpoints (either named, or using the special "last
checkpoint" name "WiredTigerCheckpoint") are read-only objects. Unless memory mapping is configured off (using the "mmap" configuration string to wiredtiger_open), read-only objects are mapped into process memory instead of being read through the WiredTiger cache. Using read-only objects where possible minimizes the amount of buffer cache memory required by WiredTiger applications and the work required for buffer cache management, as well as reducing the number of memory copies from the operating system buffer cache into application memory.